The present disclosure relates to a power tool and, more particularly, to an auto hammer for striking a fastener such as a nail.
An auto hammer is a commonly used hand-held tool, which has various types. According to the power source, the auto hammer can be divided into two types: pneumatic and electric. The pneumatic auto hammer must be equipped with an air compressor as a power supply, thus the use of the pneumatic auto hammer is limited in some occasions. The electric auto hammer comprises a transmission mechanism for converting the rotating motion of a motor into the linear motion of an impact rod arranged in a nozzle. When a switch on the auto hammer is turned on, the electric power energy is converted into the mechanical energy of the reciprocating motion.
Both U.S. Pat. No. 6,431,430 and PCT Publication No. WO 2006/008546 disclose an electric auto hammer powered by a battery pack. The described electric auto hammer comprises a slider-crank mechanism for converting the rotating motion into the linear motion. However, one disadvantage of the described auto hammer is that the slider-crank mechanism substantially performs the push actions, but not the strike actions. The efficiency of such push actions is much lower than that of the strike actions when the auto hammer is provided with the same motor power. Another disadvantage is that the stroke of a pushing rod driven by the slider-crank mechanism is a constant, so when the nail meets a hard object, the resistance force produced thereby may cause the rotor of the motor to be locked. A further disadvantage is that the motor is arranged in front of or behind the handle so that the connection between the motor and the transmission mechanism takes a lot of space which make the auto hammer relatively larger and inconvenient for a user to operate and carry.
Chinese Patent No. 1769010 discloses an auto hammer which comprises a rack and pinion mechanism for converting the rotating motion of a motor into the biasing force of a compression spring, and then the compression spring is released by a releasing mechanism to produce a striking force. The described auto hammer can carry out a single-strike action under the spring force, but not a continuous strike action. So the work efficiency is still relatively low, and the auto hammer cannot be used frequently. Furthermore, the motor is arranged in a housing below a head and separated from a handle, thus the structure of the auto hammer is still not compact.